Electrical Methods of Analysis

Electrical methods of analysis (apart from electrogravimetry referred to above) involve the measurement of current, voltage or resistance in relation to the concentration of a certain species in solution. Techniques which can be included under this general heading are (i) voltammetry (measurement of current at a micro-electrode at a specified voltage) (ii) coulometry (measurement of current and time needed to complete an electrochemical reaction or to generate sufficient material to react completely with a specified reagent) (iii) potentiometry (measurement of the potential of an electrode in equilibrium with an ion to be determined) (iv) conductimetry (measurement of the electrical conductivity of a solution). 

IE. Electrical Methods of Analysis. Among the various electrical properties which have been used for analysis and for which measuring apparatus may be directly incorporated in the reaction chamber are the dielectric constant the electrical conductance the pH by using glass, calomel, or H electrodes the redox potential and, in the case of gas reactions, the thermal conductivity. These properties are easily measured and lend themselves, as do the optical methods, to automatic recording devices. However, they also must be used only after careful calibratiomand do not give better than 1 per cent accuracy without unusual attention. 

Adams RN (1963) Voltammetry at electrodes with fixed surfaces. In Kolthoff IM, Hiving PJ and Sandell EB, eds. Treatise on analytical chemistry, Part I (Theory and practice), Vol 4, section D-2, Electrical methods of analysis (Reilley CN, section advisor), pp. 2381-2416. John Wiley Sons, New York. 

Fundamentally, introduction of a gaseous sample is the easiest option for ICP/MS because all of the sample can be passed efficiently along the inlet tube and into the center of the flame. Unfortunately, gases are mainly confined to low-molecular-mass compounds, and many of the samples that need to be examined cannot be vaporized easily. Nevertheless, there are some key analyses that are carried out in this fashion the major one i.s the generation of volatile hydrides. Other methods for volatiles are discussed below. An important method of analysis uses lasers to vaporize nonvolatile samples such as bone or ceramics. With a laser, ablated (vaporized) sample material is swept into the plasma flame before it can condense out again. Similarly, electrically heated filaments or ovens are also used to volatilize solids, the vapor of which is then swept by argon makeup gas into the plasma torch. However, for convenience, the methods of introducing solid samples are discussed fully in Part C (Chapter 17). 

X-ray intensity, see Intensity X-ray irradiance, definition, 6 X-ray methods of analysis, comparative, statistics, 254-256, 280 use of Coolidge tubes in, 6 X-ray Microscope, General Electric, 291-296... 

Coulometric methods of analysis involve measuring the quantity of electricity required to effect a quantitative chemical or electrochemical reaction and are based on Faraday s laws of electrolysis ... 

Cations form a diffuse layer of ions called the diffuse double layer or the electrical double layer around soil particles as depicted in Figure 5.10. The existence of the diffuse double layer means that the ions are not evenly distributed throughout the solution rather, cations are more concentrated close to soil particle surfaces and are less concentrated further away. This phenomenon must be kept in mind, particularly when electrochemical analytical methods of analysis are developed [5,7],... 

The subject of electrochemistry deals with the study of the chemical interaction of electricity and matter generally, but it is the interaction with solutions that is of particular value in analytical biochemistry. The electrical properties of a solution depend upon both the nature of the components and their concentration and permit qualitative and quantitative methods of analysis to be... 

Ref J. Campisi, "Development of Methods of Analysis of the Flash Charge for Electric... 

Some of these physicochemical methods of analysis were applied previously to the system sulphuric acid-nitrobenzene by Usanqvtch, Kozhina and Tartakovskaya [7], who investigated the viscosity and electrical conductivity at 0, 10, 18 and 30°C. On the basis of these results they concluded that beside the addition compound 1 1 addition compounds of the types 2 1 and 1 2 are also formed in these mixtures. The viscosity isotherm of this system is a typical example of the so-called S-isotherms, which have been the object of controversy between some Russian authors [8, 9, 10]. The surface tension of this system was investigated by Bailey [11]. 

Investigation of atomic spectra yields atomic energy levels. An important chemical application of atomic spectroscopy is in elemental analysis. Atomic absorption spectroscopy and emission spectroscopy are used for rapid, accurate quantitative analysis of most metals and some nonmetals, and have replaced the older, wet methods of analysis in many applications. One compares the intensity of a spectral line of the element being analyzed with a standard line of known intensity. In atomic absorption spectroscopy, a flame is used to vaporize the sample in emission spectroscopy, one passes a powerful electric discharge through the sample or uses a flame to produce the spectrum. Atomic spectroscopy is used clinically in the determination of Ca, Mg, K, Na, and Pb in blood samples. For details, see Robinson. 

E Electrochromatography. It is defined by Heftmann(Ref 78,p 14) as "a method of analysis in which direct current electrical potential promotes the separation of substances by differential migration from a narrow zone in a stabilized background electrolytic solution . 

The Analytical section has been subjected to some changes. An electrically heated combustion furnace, some new methods of analysis, and the method of Rast for the determination of molecular weights, are also described. Chapter XLIV. on tests for some common organic substances has been completely rewritten. 

Results of a laboratory analysis for the specific rate constant for the saponification of ethyl acetate by NaOH at 0 [ °C] are given below. One of the runs was performed with an electric stirrer, while the others were hand stirred. The results were analyzed by the differential and integral methods. Does the electric stirrer make a significant difference to the results Does the method of analysis of data make a significant difference ... 

The fact that excited atoms give off specific colors and not a rainbow of colors suggested to Niels Bohr, a Danish physicist, that electrons are permitted in only certain locations within the atom. These locations are called energy levels. Each element behaves in its own unique way when excited by heat or electricity and produces a very specific pattern of lines of color called the atomic spectrum of that element (Figure 8.5). This unique chemical fingerprint is the foundation of atomic spectroscopy, a method of analysis used by forensic and medical laboratories to identify elements... 

Ref J. Campisi, "Development of Methods of Analysis of the Flash Charge for Electric Squib , Report from the Chemical Laboratory of Picatinny Arsenal, Dover, NJ, Rept No 126836, 14 July, 1949... 

The physical methods of analysis are based on the measurement of electrical and thermal characteristzics. 

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